1. Field of the Invention
The present invention relates to communication systems, in particular, modulating physical channels in Evolved Universal Terrestrial Access (E-UTRA) systems.
2. Description of the Related Art
Mobile stations, such as cellular handsets, rely on radio access technologies to communicate with a core network. A core network is the central part of a telecommunications network, providing services to connected customers. Evolved Universal Terrestrial Access (E-UTRA) is an International Telecommunications radio access network standard optimizing the transfer of packet data. E-UTRA is found in communications such as 4G mobile telecommunications networks. E-UTRA has been developed into a complete set of specifications. Specifically, details on E-UTRA physical channels and modulation are described in “3rd Generation Partnership Project (3GPP); Technical Specification Group Radio Access Network; E-UTRA; Physical Channels and Modulation (3GPP TS 36.211)”, hereinafter referred to as “3GPP TS 36.211”. 3GPP TS 36.211 defines modulation schemes with a layer mapping algorithm for physical channels.
In general, a channel refers to a communications link connecting two network nodes (e.g., a base station and a cellular handset). The physical channel refers to the means for transmitting and receiving raw bits across a network. A physical channel might group a bit stream into code words or symbols and convert the bit stream into a physical signal that is transmitted over a hardware transmission medium. A property of a physical channel is its modulation scheme, used to convey a message signal inside a carrier signal that can be physically transmitted. 3GPP TS 36.211 describes modulation schemes that first receives binary digits as input and produces complex-valued modulation symbols as output. The symbols are mapped onto one or more transmission layers where a gain and/or an order permutation might be applied. After the mapping, the complex-valued modulation symbols on each layer are precoded for transmission on the antenna ports.
According to the 3GPP TS 36.211, the multi-layer mapping and the precoding processes start after the modulation of bits is complete, thus the multi-layer mapping and precoding processes are performed as distinct processes in the standard. Implementing the modulation schemes using distinct processes as described in the specification documents results in increased processing times. Increased processing times might result in unacceptable system latency and bit rate values.